Humans use lichens for a variety of interests. They are known to produce antibiotics and essential oils used for perfumes. Historically, dyes were extracted from lichens for use in litmus paper. Lichens have scientific names as though they are a species of organism, but actually a lichen is a fungus and an alga living in a symbiotic relationship both are benefited by living together. The fungus cannot photosynthesize so it cannot create food from solar energy, but the alga can photosynthesize.
The alga needs water but cannot hold it well, but the fungus is like a sponge more able to absorb and hold moisture. Thus, both species get their limiting resources from each other. There are three major growth forms of lichens. The crustose crusty form adheres so tightly to the substrate that it is impossible to remove without destroying the lichen.
He explains that he has identified the infection as a fungus, and that the antifungal cream works against the most common fungi associated with ringworm. However, the cream may not work against some species of fungus. If the cream is not working after a couple of weeks, Anthony should come in for another visit, at which time the doctor will take steps to identify the species of the fungus.
Positive identification of dermatophytes requires culturing. These features suggest that the fungus is Trichophyton rubrum , a common cause of ringworm. Skip to main content. The Eukaryotes of Microbiology. Search for:. Lichens Learning Objectives Explain why lichens are included in the study of microbiology Describe the unique characteristics of a lichen and the role of each partner in the symbiotic relationship of a lichen Describe ways in which lichens are beneficial to the environment.
Think about It What types of organisms are found in lichens? What are the three growth forms of lichens? Key Concepts and Summary Lichens are a symbiotic association between a fungus and an algae or a cyanobacterium The symbiotic association found in lichens is currently considered to be a controlled parasitism , in which the fungus benefits and the algae or cyanobacterium is harmed Lichens are slow growing and can live for centuries in a variety of habitats Lichens are environmentally important, helping to create soil, providing food, and acting as indicators of air pollution.
Multiple Choice You encounter a lichen with leafy structures. Which term describes this lichen? This lichen is a foliose. Show Answer Answer a. The cortex is the outer layer of a lichen. Show Answer Answer b. The fungus in a lichen is an ascomycete. Lastly, there are many lineages of lichen fungi that are parasitic on other lichens — the so-called lichenicolous lichens!
In some cases, non-lichen fungi have evolved from lichenised forms. These can be specialised opportunistic parasites or saprophytes or even symbionts, competing for nutrients with other fungi in the lichen thallus.
The symbiosis may be more complex than this. Recent work by Spribille et al has found yeasts embedded in the cortex of ascomycete macrolichens, and their abundance correlates with previously unexplained variations in phenotype. There is also convincing evidence for a consistent presence of non-photosynthetic bacteria within the thalli of all lichens, although the role of these bacteria is as yet unknown.
Interestingly, a role for non-photosynthetic bacteria was suspected for many years, as the relichenization of separately cultured fungi and algae in the lab was facilitated by the presence of bacteria. In fact, a legacy of exclusion from accepted mycological research persisted until the s, despite their obvious affinities with non-lichen fungi. With the advent of molecular biology, the shared history of lichens and non-lichens has been elucidated and accepted , and we now know that the fungi that form lichens have evolved from many only distantly related lineages across the fungal tree of life, uniting them and their non-lichen relatives in the Kingdom Fungi.
Lichen fungi are a heterogeneous group; they are similar only ecologically, in that they share the nutritional strategy of gaining carbon from an internal symbiotic photosynthetic partner, the photobiont. In the study of lichens, the name and classification belongs to the fungal partner, which in most cases is the dominant member of the association, at least in terms of biomass.
Lichen fungi have evolved independently several times within the mushroom-forming fungi and relatives the basidiomycetes , but much more commonly, from within the cup fungi the ascomycetes. Probably more than ten distinct major lineages of fungi within the ascomycetes are lichenised. Current estimates suggest that one fifth of all known fungi and half of all ascomycetes are lichenised, with about 28, species worldwide.
As with most organisms, lichen fungi are most diverse and least studied in the tropics. For example, the genus Arthonia is comprised of a mix of lichenised and non-lichenised species and includes many which are specialist parasites, only found on one or a few closely-related host lichens. In a single genus, then, we have a case of lichen parasites evolving from lichen fungi! Other non-lichen fungi arose from lichenised ancestors, such as Stictis and Ostropa.
Fungi are classified in part by the type of spore-producing structures they produce, with the cup fungi ascomycetes named for the open, cup-shaped structures which often bear the sexual spores of the fungi. Not all ascomycetes have these cup-shaped structures, however, and, easily observed morphological characteristics like fruit type cup-like apothecia versus flask-shaped perithecia, for example cannot always be used to assess relationships.
Unfortunately, this means that not all fungi sharing a single characteristic are likely to be related. However, some order can be distilled. The bulk of lichen diversity belongs to the class including the well-known genera Lecanora , Cladonia , Parmelia and Peltigera Lecanoromycetes, or the Lecanora -group , where spores are borne mostly in open or cup-shaped fruits apothecia. This group of fungi is very old, estimated to have evolved during the Carboniferous period.
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